The present invention relates to robot arm mechanisms and, in particular, to a self-teaching robot arm positioning method that determines whether there exists misalignment of a specimen holder relative to a robot arm mechanism to prevent the robot arm from reaching toward an unintended location on the specimen holder.
Currently available robot arm mechanisms include pivotally joined multiple links that are driven by a first motor and are mechanically coupled to effect straight line movement of an end effector or hand and are equipped with a second, independently operating motor to angularly displace the hand about a central axis. Certain robot arm mechanisms are equipped with telescoping mechanisms that move the hand also in a direction perpendicular to the plane of straight line movement and angular displacement of the hand. The hand is provided with a vacuum outlet that secures a specimen, such as a semiconductor wafer, computer hard disk, or compact disk, to the hand as it transports the specimen between processing stations.
U.S. Pat. No. 4,897,015 of Abbe et al. describes a rotary-to-linear motion robot arm that uses a first motor to control a multi-linkage robot arm to produce straight line radial motion from motor-driven rotary motion. An additional motor may be coupled to the robot arm for operation independent of that of the first motor to angularly move the multi-linkage robot arm without radial motion. Because they independently produce radial motion and angular motion, the first and second motors produce useful robot arm movement when either one of them is operating.
The robot arm of the Abbe et al. patent extends and retracts an end effector (or a hand) along a straight line path by means of a mechanism that pivotally couples in a fixed relationship a first arm (or forearm) and a second (or upper) arm so that they move in predetermined directions in response to rotation of the upper arm. To achieve angular displacement of the hand, a xcex8 drive motor rotates the entire robot arm structure. The Abbe et al. patent describes no capability of the robot arm to reach around corners or travel along any path other than a straight line or a circular segment defined by a fixed radius.
U.S. Pat. No. 5,007,784 of Genov et al. describes a robot arm with an end effector structure that has two oppositely extending-hands, each of which is capable of picking up and transporting a specimen. The end effector structure has a central portion that is centrally pivotally mounted about the distal end of a second link or forearm. The extent of pivotal movement about all pivot axes is purposefully limited to prevent damage to vacuum pressure flexible conduits resulting from kinking or twisting caused by over-rotation in a single direction.
The coupling mechanism of a first link or upper arm, the forearm, and the end effector structure of the robot arm of the Genov et al. patent is more complex than that of the robot arm of the Abbe et al. patent. Nevertheless, the robot arm structures of the Abbe et al. and Genov et al. patents operate similarly in that each of the end effector structures picks up and transports specimens by using one motor to extend and retract a hand and another, different motor to rotate the entire robot arm structure to allow the hand to extend and retract at different ones of a restricted number of angular positions.
Robot arms of the type described by the Abbe et al. and Genov et al. patents secure a specimen to the hand by-means of vacuum pressure delivered to the hand through fluid conduits extending through the upper arm, forearm, and hand and around all of the pivot axes. The Abbe et al. patent is silent about a vacuum pressure delivery system, and the Genov et al. patent describes the use of flexible fluid conduits. The presence of flexible fluid conduits limits robot arm travel path planning because unidirectional robot arm link rotation about the pivot axes xe2x80x9cwinds upxe2x80x9d the conduits and eventually causes them to break. Thus, conduit breakage prevention requirements prohibit-continuous robot arm rotation about any of the pivot axes and necessitate rewind maneuvers and travel path xe2x80x9clockoutxe2x80x9d spaces as part of robot arm travel path planning. The consequences of such rewind maneuvers are more complex and limited travel path planning, reduced throughput resulting from rewind time, and reduced available work space because of the lockout spaces.
Moreover, subject to lockout space constraints, commercial embodiments of such robot arms have delivered specimens to and retrieve specimens from stations angularly positioned about paths defined only by radial distances from the axes of rotation of the robot arms.
Thus, the robot arm structures described by the Abbe et al. and Genov et al. patents are incapable of transporting specimens between processing stations positioned in compact, irregularly shaped working spaces. For example, neither of these robot arm structures is set up to remove specimen wafers from and place specimen wafers in wafer cassettes having their openings positioned side-by-side in a straight line arrangement of a tightly packed working space.
Wafer cassettes are usually positioned side by side on a support structure along a radial path measured from the central axis of or along a straight line distance from the robot arm mechanism. These wafer cassettes are often misaligned from their nominal cassette opening arrangements relative to the robot arm mechanism. Such misalignment could cause a robot arm mechanism to direct the hand or the wafer it carries to strike the cassette instead of extend into its opening to, respectively, remove or replace a wafer. Robot arm mechanism contact with the cassette resulting from alignment offset can, therefore, create contaminant particles.
An object of the invention is, therefore, to provide a multiple link robot arm system that has straight line motion, extended reach, corner reacharound, and continuous bidirectional rotation capabilities for transporting specimens to virtually any location in an available work space that is free of lockout spaces.
Another object of the invention is to provide such a system that increases specimen processing throughput in the absence of robot arm rewind time and radial positioning of processing station requirements.
A further object of this invention is to provide such a system that is capable of continuous rotation in either direction with no susceptibility to kinking, twisting, or breaking of conduits delivering vacuum pressure to the hand.
Still another object of the invention is to provide such a system that uses two motors capable of synchronous operation and a linkage coupling mechanism that permit a hand of an end effector structure to change its extension as the multiple link robot arm mechanism to which the hand is associated changes its angular position.
Yet another object of the invention is to provide a system component misalignment correction technique for either mechanical alignment of system it components or robot arm mechanism trajectory control to compensate for support structure alignment offset.
Each of two preferred embodiments of the present invention includes two end effectors or hands. A first embodiment comprises two multiple link robot arm mechanisms mounted on a torso link that is capable of 360 degree rotation about a central or xe2x80x9ctorsoxe2x80x9d axis. Each robot arm mechanism includes an end effector having a single hand. A second embodiment is a modification of the first embodiment in that the former has one of the robot arm mechanisms removed from the torso link and substitutes on the remaining robot arm mechanism an end effector with oppositely extending hands for the end effector having a single hand.
Each of the multiple link robot arm mechanisms of the first and second embodiments uses two motors capable of synchronized operation to permit movement of the robot arm hand along a curvilinear path as the extension of the hand changes. A first motor rotates a forearm about an elbow axis that extends through distal and proximal ends of the upper arm and forearm, respectively, and a second motor rotates an upper arm about a shoulder axis that extends through a proximal end of the upper arm. A mechanical linkage couples the upper arm and the forearm. The mechanical linkage forms an active drive link and a passive drive link. The active drive link operatively connects the first motor and the forearm to cause the forearm to rotate about the elbow axis in response to the first motor. The passive drive link operatively connects the forearm and the hand to cause the hand to rotate about a wrist axis in response to rotation of the forearm about the elbow axis. The wrist axis extends through distal and proximal ends of the forearm and hand, respectively.
In two embodiments described in detail below, a motor controller controls the first and second motors in two preferred operational states to enable the robot arm mechanism to perform two principal motion sequences. The first operational state maintains the position of the first motor and rotates the second motor so that the mechanical linkage causes linear displacement (i.e., extension or retraction) of the hand. The second operational state rotates the first and second motors so that the mechanical linkage causes angular displacement of the hand about the shoulder axis. The second operational state can provide an indefinite number of travel paths for the hand, depending on coordination of the control of the first and second motors.
Whenever the first and second motors move equal angular distances, the angular displacement of the upper arm about the shoulder axis and the angular displacement of the forearm about the elbow axis equally offset and thereby result in only a net angular displacement of the hand about the shoulder axis. Thus, under these conditions, there is no linear displacement of the hand and no rotation of the hand about the wrist axis. Whenever the first and second motors move different angular distances, the angular displacement of the upper arm about the shoulder axis and the angular displacement of the forearm about the elbow axis only partly offset and thereby result in angular displacements of the hand about the shoulder and wrist axes and consequently a linear is displacement of the hand. Coordination of the position control of the first and second motors enables the robot arm mechanism to describe a compound curvilinear path of travel for the hand.
A third or torso motor rotates the torso link about the central axis, which extends through the center of the torso link and is equidistant from the shoulder axes of the robot arm mechanisms of the first embodiment. The motor controller controls the operation of the torso motor to permit rotation of the torso link independent of the motion of the robot arm mechanism or mechanisms mounted to it. The presence of the rotatable torso link together with the independent robot arm motion permits simple, nonradial positioning of specimen processing stations relative to the torso axis, extended paddle reach, and corner reacharound capabilities. The consequence is a high speed, high throughput robot arm system that operates in a compact work space.
Each of the robot arm mechanisms of the first embodiment is equipped with a rotary fluid slip ring acting as a fluid feedthrough conduit. These slip rings permit the hand to rotate continuously in a single direction as the robot arm links rotate continuously about the shoulder, elbow, and wrist axes without a need to unwind to prevent kinking or twisting of fluid pressure lines. Vacuum pressure is typically delivered through the fluid pressure lines.
The robot arm mechanism of the second embodiment is equipped with a rotary fluid multiple-passageway spool that delivers fluid pressure separately to each rotary joint of and permits continuous rotation of the robot arm links in a single direction about the central, shoulder, elbow, and wrist axes.
Preferred embodiments implementing the self-teaching robot arm positioning method to compensate for support structure alignment offset need not include two end effectors or hands. A misalignment correction technique carried out in accordance with the invention entails the use of a component emulating fixture preferably having mounting features that are matable to support structure mounting elements. The emulating fixture preferably includes two upwardly extending, cylindrical locating features that are positioned to engage a fork-shaped end effector in two different extension positions. The robot arm positioning method is self teaching in that the motor angular position data measured relative to the fixture features are substituted into stored mathematical expressions representing robot arm mechanism motion to provide robot arm position output information that determines the alignment position of the wafer carrier and thereby the existence of error in its actual alignment relative to a nominal alignment.
For manual correction, robot arm mechanism position output information provides the angular offset between the actual and nominal radial distances between the robot arm mechanism shoulder axis and the two locating features. Position coordinates for proper alignment by manual repositioning of any misaligned wafer carrier can then be derived. For automatic correction, robot arm mechanism position output information is used to derive a trajectory that causes the end effector to properly access the wafers stored in a misaligned wafer carrier.
Additional objects and advantages of this invention will be apparent from the following detailed description of preferred embodiments thereof which proceeds with reference to the accompanying drawings.